1. Field of the Invention
The present invention relates to the sealing of a clearance between a host pipe and a liner pipe.
2. Discussion of the Background
It is known to line host pipes with liner pipes to replace or repair the host pipe because the host pipe is already defective in some way or may become defective and fluid may be leaking from it or be about to leak from it.
Where the host pipe is a gas carrying service pipe supplying gas from an external main to a building such as a dwelling, the liner pipe is normally of plastic eg polyethylene and the service pipe of steel.
To replace the service pipe, the liner pipe is fed into a downstream (in the sense of the direction of gas flow) end of the service pipe into and then along the service pipe until the desired length of service pipe has been replaced. To permit the easy passage of the liner pipe into and along the service pipe the external diameter of the liner pipe and the internal diameter of the service pipe are chosen so that there is a clearance between the pipes.
A so-called xe2x80x9cnose-conexe2x80x9d is connected to the leading end of the liner pipe before it is fed into the service pipe. This is a tubular member of the plastics material which in use, may be adhered to or force fitted onto the leading end of the liner pipe. The nose-cone is provided with at least one vane or fin radially directed outwardly from the body of the member. The vane or vanes are flexible and, in use, engage the internal wall of host pipe to provide a seal or barrier to the flow of gas along the clearance from the upstream to the downstream end of the clearance both while the liner pipe is being fed into the host pipe as well as after the feeding step has been completed.
The nose-cone is also provided with a frangible means to block the bore of the nose-cone while it and the liner pipe are being fed into and along the service pipe. This temporarily prevents gas entering the liner pipe.
The frangible means may take the form of a frangible membrane or a push-out or pop-out stopper or plug. When the liner pipe is in place the membrane is ruptured and/or removed or the stopper pushed out to permit gas to enter the liner pipe.
Then a sealant is introduced into the clearance to form a further seal in the clearance. The sealant may be a two-part anaerobic sealant which while fluid is injected into the clearance and then sets or hardens after a delay.
A full description of a typical service pipe replacement technique is described in UK Published Patent Application No. 2227071A together with a typical nose-cone.
Another method and nose-cone is described in UK Published Patent Application No. 2275901A.
The sealant used in the two documents referred to above is relatively expensive and a significant amount of it must be used to ensure a gas-tight seal.
It is therefore an object of the present invention to seal the clearance between a host pipe and a liner pipe in a less expensive manner than is described in the above documents.
According to one aspect of the present invention, there is provided apparatus for sealing a clearance between a host pipe and a liner pipe which, in use, is fed into the host pipe, the apparatus comprising a tubular element for connection to or forming a leading end of the liner pipe and a compressible seal which is adapted when compressed longitudinally to expand radially and which, in use, is mounted on the element, the arrangement being such that the seal moves freely with the element in the direction of feeding of the liner pipe but when the liner pipe is retracted counter to the direction of feeding further seal movement is arrested and the seal is compressed longitudinally by the element so that the seal expands radially to engage the internal wall of the host pipe and seal the clearance.
According to another aspect of the present invention, there is provided a method for sealing a clearance between a host pipe and a liner pipe which, in use, is fed into the host pipe, the method comprising, after the liner pipe has been fed into the host pipe, causing a compressible seal mounted on a leading end of the liner pipe to be compressed longitudinally so that the seal expands radially to engage the internal wall of the host pipe and seal the clearance.
Preferably the seal is annular in shape.
The seal may be porous and may also be in the form of a sponge possibly of foam plastic or the like.
A sealant is suitably provided in liquid form for application to the seal, the sealant, in use, on being applied to the seal permeating the pores of the seal before the seal is fed into the host pipe and then setting after a time which allows the seal to be fed into the host pipe, compressed and expanded radially into engagement with the internal wall of the host pipe.
The sealant maybe a two part sealant conveniently of the anaerobic kind which sets some time after the components have been mixed, the time of setting being variable dependent on the initial proportion of the components.
Preferably the tubular element is provided with first and second stop means between which, in use, the seal is compressed.
The first of the stop means is suitably located forwardly of the second stop means which is slidably mounted on the element and is adapted, in use, to move with the element in the direction of feeding of the liner pipe but is also adapted to grip the internal wall of the host pipe and remain stationary during the rearward movement of the liner pipe when this is retracted so that the seal is compressed between the two stop means.
Conveniently the first stop means is a nose-cone for connection to the leading end of the tubular element.
The nose-cone may be similar to any of those referred to in the introduction.